FIG. 12 is a schematic block diagram of a motor driving device disclosed in Patent Document 1. In the motor driving device shown in FIG. 12, a control device 30 receives a power-supply current Ib from a current sensor 11 and a reactor current IL from a current sensor 18. The control device 30 detects a maximum value ILmax and a minimum value ILmin based on the reactor current IL, and determines, based on the detected maximum value ILmax and minimum value ILmin and the power-supply current Ib, whether the reactor current IL crosses a zero point or not. When the reactor current IL crosses the zero point, the control device 30 generates a signal PWMS and outputs the generated signal PWMS to a boost converter 12. The boost converter 12 stops a boosting operation or a bucking operation based on a switching operation in accordance with the signal PWMS.
FIG. 13 is a circuit diagram showing a control system for DC/DC converter disclosed in Patent Document 2. In the control system shown in FIG. 13, when the voltage of a DC power supply 1 is converted into a constant-voltage DC output by ON/OFF operation of a switching element 2 and an oscillation period and a forced stop period are provided at a light load including no load to oscillate the switching element 2 intermittently, a signal outputted from an output voltage detecting and regulating circuit 6 for controlling an output voltage to be constant is used as a first command value for determining ON/OFF timing of the switching element 2 and a comparison signal for comparing the first command value with a constant-frequency triangular wave or saw-tooth wave signal is used as a control signal for controlling the oscillation period and forced stop period of the switching element 2 at the light load including no load. According to the control system, switching loss and conduction loss at a light load including no load on the DC/DC converter can be reduced.